Hydraulic servo valve



Sept. 17, 1968 w, VEU ER ET AL 3,401,601

HYDRAULIC SERVO VALVE Original Filed Jan. 25, 1965 INVEN 0R5 & 24' ll "i 17 POWER HYDRAULIC PUMP 5g CONTROLLER LOAD E 1% Q iio /7- D: )a- Lu 5 \i G .1

WENCEL l VELICER UgBAN A. WEBER ORFICE GAP A i-foggy.

United States Patent Office 3,401,601 Patented Sept. 17, 1968 3,401,601 HYDRAULIC SERVO VALVE Wencel J. Velicer, Milwaukee, and Urban A. Weber,

Brookfield, Wis., assignors to Johnson Service Company, Milwaukee, Wis., a corporation of Wisconsin Continuation of application Ser. No. 427,592, Jan. 25,

1965. This application Jan. 23, 1967, Ser. No, 622,380

5 Claims. (Cl. 91-47) ABSTRACT OF THE DISCLOSURE A constant displacement pump is connected to a piston type hydraulic actuator via a servo valve having an electromagnetically positioned leak port for physically positioning a damper, valve or other load. A special restrictor in the form of a tubular restrictor for optimum results is inserted between the servo valve and the actuator to control the relationship between the magnetic torque and the hydraulic torque acting on the leak port.

This application is a continuation application of appli cation Ser. No. 427,592, which was filed Jan. 25, 1965, now abandoned, and entitled, Hydraulic Servo Valve.

This invention relates to a hydraulic servo valve and particularly to a hydraulic servo valve controlled by an electromagnet for accurate setting transmission of hydraulic pressure to a hydraulic actuator.

The use of hydraulic actuators in the control of various loads has many advantages from the standpoint of reliability and stability of load operations. Generally, the op eration or energizing of a load is controlled by controlling the transmission of fluid pressure or flow to a hydraulic actuator. A very common system employs a servo valve including a flapper or lid selectively positioned over a leak port to selectively bypass the operating fluid from the system and thereby throttle the pressure supplied to the hydraulic actuator. The flapper or valve may be positioned in any suitable manner; for example, through the use of an electromagnet having a pivotally mounted armature unit upon which the lid is mounted. Under steady state conditions, the balance condition is determined by the magnetic torque produced by the electromagnet and the hydraulic torque produced by the hydraulic fluid on the lever. An increase in the energization of the electromagnet will increase the magnetic torque and move the lid to either close or open the nozzle or the leak port depending upon the particular construction and pivot point arrangement. The pressure increases and decreases as the leak port is closed and opened until the hydraulic and magnetic torque established on the armature unit are again equal. For example, a highly satisfactory electrohydraulic actuator is disclosed in US. Patent No. 3.046,743 to B. Burley.

In electrohydraulic actuators and the like employing the leak port principle, maximum response with stable operation has presented continuing difficulties. Stability appears to have presented a particular problem over a wide range of fluid temperatures because of the variation of the viscosity with the temperature. Further, the minimum pressure which can be established in the pneumatic actuator, defined as the residual pressure, is generally dependent solely on the characteristics of the pump and of the leak port including the lid or the lever controlling the lid and the nozzle or leak orifice. This has been found to generally limit the range over which modulation of pressure can be obtained.

The present invention is particularly directed to a very simple and reliable means for providing a leak port type hydraulic servo valve having improved stability and pressure response over a wide modulation range.

In accordance with the present invention, the connection between the hydraulic actuator and the leak port reference chamber includes a tubular restrictor which with the chamber of the hydraulic actuator defines a fluid resistor-capacitor network and introduces a time constant into the operation of the hydraulic actuator.

In accordance with the present invention, the restrictor is selected such that as the leak port opens from a set position, the magnetic torque is maintained greater than the hydraulic torque; that is, the magnetic torque curve has a lesser slope than the hydraulic torque curve and the two curves intersect at the preset position. The restrictor also reduces or minimizes the effect of transient hydraulic torques, which would tend to destroy the above desired relationship, resulting from increased rates of momentum change as the lid opens. Although an orifice can be employed, its resistance varies with the flow whereas a tubular restrictor provides a desirable preset resistance. Additionally, in accordance with the present invention, a suitable restrictor or orifice is introduced between the pump and the servo valve to reduce the residual pressure. The orifice diameter is made as small as required to produce the desired residual pressure and thereby increase the range over which modulation may be provided while maintaining stable operations.

The present invention thus provides a highly improved and simplified hydraulic servo valve particularly employing an electromagnetic positioner or other device having a similar characteristic.

The drawing furnished herewith illustrates a preferred construction of an electrohydraulic valve having the above features and advantages as Well as others which will be clear from the following description.

In the drawing:

FIG. 1 is a diagrammatic illustration of a hydraulic servo system for controlling a load and employing a servo valve constructed in accordance with this invention;

FIG. 2 is an enlarged fragmentary view of the servo valve unit; and

FIG. 3 is a graphical illustration showing hydraulic and magnetic torque characteristics.

Referring to FIG. 1, a hydraulic pump 1 such as a constant displacement vane type pump is shown in block diagram as a source of oil or other hydraulic fluid suitable as an operating fluid to develop actuating pressures within a hydraulic actuator 2 which is connected to position a desired load 3, for example, a damper or valve in temperature controlling systems. An electrohydraulic servo valve unit 4 interconnects the pump 1 to the actuator 2 and includes a reference chamber 5 through which the hydraulic fluid is transmitted from the pump 1 to the actuator 2. The valve unit 4 includes a leak port 6 connected to the reference chamber 5 with an adjustably positioned lid 7 disposed over the leak port for throttling of the pressure transmitted to the actuator 2. The lid 7 is positioned by an electromagnet assembly '8 which is connected in series with a controller 9 to a suitable power source. The controller 9 is coupled to the load 3, as dia grammatically shown, and positioned thereby to energize assembly 8 in accordance with a preselected set point operation.

Generally, the embodiment of the invention operates in accordance with well known servo theories. The valve unit 4 is set at a preset point to throttle a selected portion of the pressure from the pump 1 and hold the actuator 2 and therefore load 3 at a preset position or condition. If the load varies from the predetermined set point for any reason, the load actuates the controller 9 which varies the power transmitted to the electromagnet assembly 8 to vary the position of the lid 7 in a direction to change the throttling of the transmitted pressure to reposition the hydraulic actuator 2 and thereby the load 3 toward the set point.

The present invention is particularly directed to improvind the response and stability of the system as more fully described hereinafter.

In the illustrated embodiment of the invention, the output port of the pump 1, which includes an orifice 10, is connected by an input coupling line 11 to an input port 12 of the unit 4 from which the fluid passes either to the leak port 6 or the actuator 2.

The illustrated actuator 2 is diagrammatically shown as a piston unit including a piston 13 within a fixed cylinder 14. The piston 13 is spring biased, as by a spring 15, toward the head 16 of the cylinder 12 and coupled to the load 3 to correspondingly position or otherwise control it. The head 16 is provided with a central upstanding tubular projection 17 to which unit 4 is mounted for fluid transmission through an opening 18 in the head.

The illustrated servo valve unit 4 includes a generally round tubular body 19 corresponding to projection 17 and projecting outwardly therefrom. A reference chamber is formed within the upper portion of body 19 with an input nozzle or port 12 projecting laterally therefrom and connected to the coupling line 11. The leak port 6 is press fitted or otherwise secured within the uppermost end of the tubular body 19 and includes a suitable throttling orifice 20 over which the lid 7 is variably positioned in a vertical direction.

The lower end of the tubular body portion 19 constitutes the output port and is interconnected to the upstanding projection 17 by a fluid restrictor assembly 21 which particularly illustrates the subject matter of the present invention.

In the illustrated embodiment of the invention, the lid 7 is secured to the electromagnet assembly -8 by a threaded stud 22 which projects upwardly from the back of the lid through an opening in an armature plate or lever 23 and a threaded nut 24 secured to the underside thereof. The relative position of lid 7 with respect to the orifice 20 may therefore be selectively adjusted and locked in place with respect to the orifice by a lock nut 25 threaded onto the stud, in a known manner, for actuation by assembly 8.

The assembly 8 includes an L-shaped mounting bracket 26 extending as an integral lateral extension of the uppermost end of the tubular body 19 with an upstanding support arm 27 terminating outwardly of the leak port 6. The armature plate or lever 23 is secured to the upper end of the support arm 27 by a flexture hinge 28 or the like and extends laterally therefrom to position the lid 7 overlying orifice 20 of leak port 6. A U-shaped magnetic core 29 is secured to the bracket with a Winding 30 encircling one leg of the core. An armature 31 is secured to the underside of the plate or lever 23 and spans the core 29 to complete the magnetic path through the magnetic core in accordance with known construction. A counter balance member 32 is shown secured to an extended portion of the lever 23 on the opposite side of the hinge 28. Thus, as the winding is energized, the armature 31 and attached lever 23 are attracted to core 29 such that the attached lid 7 is moved toward the leak port 6 to close the orifice 20 and increase the pressure and fluid transmitted to the actuator 2 through the restrictor unit 21 against the hydraulic forces created by pump 1 and actuator 2.

In the illustrated embodiment of the invention, the restrictor unit 21 includes a cylindrical tube 33 mounted within the aligned end of the cylinder head projection 17 and lower end of the valve body 6. Tube 33 is press fitted or otherwise secured within similar spaced annular support members 34 and 35 which in turn are similarly secured to projection 17 and valve body 6. The tube 33 is a fluid resistance element selected to provide maximum response with stability of operation, as subsequently described.

The orifice or opening 18 in the cylinder head includes a slanted positioning surface 36 with the bottom edge aligned with the outer periphery of tube 33. This provides a positive stop for tube 33 and eliminates any danger of the tube 33 being forced into the cylinder chamber. In operation, the system may be established with a selected set point with the lid '7 spaced a predetermined distance from orifice 20 to establish an intermediate position of piston 13. If the load 3 varies, the controller 9 changes energization of the electromagnet winding 30 and thereby repositions the lid 7. This varies the throttle effect at orifice 20 and the pressure in fluid in the cylinder chamber of actuator 2 with a corresponding repositioning of the piston.

The torque characteristics for stable operation are typically illustrated in FIG. 3 with an arbitrarily selected set point 37.

In FIG. 3, the value of the several torques acting upon the lever 23 are shown on the vertical axis with respect to the position of the lever 23 and lid 7 with respect to the leak port orifice 20. The magnetic torque line 38 varies with the length of the gap for any given constant current, in accordance with the general inverse square law. The magnetic torque will also vary and in order to maintain stable operation must be maintained with a greater negative slope such as typically shown by line 39. With the illustrated arrangement, if the lid 7 should open due to vibration or the like, the hydraulic torque decreases more rapidly than the magnetic torque and the lid 7 will return to the set point. However, as the lid 7 opens and allows a more ready escape of the fluid, the transient forces resulting from the spring loaded actuator 2 tend to increase the flow with a positive feedback action such that the hydraulic torque line follows the dotted trace line 40, which lies above the torque trace 38 of the electromagnet. Thus, as the lid 7 opens, due to vibration or the like, the momentum of the escaping fluid changes and the hydraulic forces change as the rate of change of momentum in a positive direction such that the spring loaded actuator 2 tends to evacuate the reference chamber 5 and the actuator 2. The restrictor 33 provides a preselected fluid resistance in the circuit of the actuator and forms a time constant circuit. The applicants have found that this will eliminate or essentially reduce the transient force effects and produce the stable hydraulic torque line 39 over the modulation range.

The orifice 10 in the output port of the pump reduces the residual pressure of the system, i.e., the minimum pressure which can be established in the hydraulic operator 2. For example, a pump 1 may normally produce a pressure output range of from 10 p.s.i. (pounds per square inch) to 40 p.s.i. This would permit modulation over 30 p.s.i. with a corresponding load operation. The orifice 10 permits reduction to a lower limit; for example, 2 p.s.i. The maximum pressure which would be established with orifice 20 closed by lid 7 remains the same and the modulation range increases to 38 p.s.i. The diameter of orifice 10 is selected as small as necessary to provide a preselected minimum pressure.

An electrohydraulic actuator 2 constructed in accordance with the teaching of this invention has been employed and operated satisfactorily at such pressure levels with a leak port 6 having an internal diameter at the upper end of the orifice 20 of essentially .100 inch. An orifice 10 of .040 inch was connected in the discharge port of the pump 1. A tubular restrictor 33 of 1% inches in length was mounted as shown in the drawing and had an internal diameter of essentially .042 inch. It was found that the system provided a very stable operation over a wide range of fluid temperatures as a result of the insertion of the tubular restrictor and further that the range over whichthe pressure could be modulated was increased by reducing the residual pressure attainable in the hydraulic operator.

As previously noted, an orifice might be employed rather than a tubular restrictor, that is a fluid resistance passage having a substantially greater length than its diameter. However, the resistance is not constant due to the nonlinear flow versus pressure characteristic and an orifice is not generally as desirable as the tubular restrictor.

The present invention thus provides a very simple and reliable means for optimizing the stability and response of the system with an increased range of modulationv Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim:

1. In a hydraulically actuated apparatus for actuating a hydraulic actuator, the improvement comprising a pressurized hydraulic source means,

a hydraulic valve including an input port connected to the hydraulic source means and having a leak port and a control port,

an electromagnetic means including a member overlying the leak port and having a winding adapted to be continuously energized at any one of a plurality of levels to selectively position said member with respect to the leak port and continuously vary the opening of the leak port at intermediate positions between a completely closed position and a completely open position in accordance with the energization of said electromagnetic winding, said member being essentially coupled solely to the electromagnetic means and the liquid issuing from the leak port and thereby positioned solely in accordance with the opposing forces established by the energization of said winding and the hydraulic force of the liquid at said leak port,

means to modulate the energization of the winding,

a hydraulic actuator having an operating chamber and a resiliently loaded mechanical operator forming a part of said chamber and being movable for directly mechanically positioning a load in accordance with the pressure in said chamber, and

an output control connection to the control port for connection to the operating chamber of the actuator and including a restrictor means between the control port and the actuator to control the hydraulic torque characteristic and thereby the response time with respect to the actuator.

2. The hydraulic valve apparatus of claim 1 wherein said output control connection includes a conduit connected between the control port and the actuator and a restrictor means is mounted within the conduit to regulate the response of the unit with variations in the movement of the lid, said restrictor means establishing a hydraulic torque characteristic changing at a rate greater than the electromagnetic torque characteristics for all movement of the member overlying the leak port.

3. The hydraulic apparatus of claim 2 wherein said restrictor is a tubular restrictor having a flow passageway of a length which is a substantial multiple of the diameter of the flow passageway to provide a more linear restriction.

4. The hydraulic apparatus of claim 3 wherein an orifice means is connected between the source means and the input port to reduce the pressure from the source means.

5. The hydraulic apparatus of claim 1 wherein said source is a constant displacement pump.

References Cited UNITED STATES PATENTS 2,625,136 1/1953 Moog 137-625.61 2,844,158 7/1958 Carson 91-47 3,046,743 7/1962 Burley -52 3,099,995 2/1963 Raufenbarth 91-47 XR EDGAR W. GEOGHEGAN, Primary Examiner. 

